Active cooling techniques for coiled nylon actuators

摘要

Low-cost, highly versatile thermally driven coiled nylon actuators have demonstrated great tensile stress (>10 MPa) and large stroke (>5%). The work density of this material is 100 times greater than mammalian muscle, which makes coiled nylon actuators good candidates for applications in soft robotics. Similar to other thermally driven actuators, heat transfer rate limits their frequency response and benefits from extensive cooling. The cooling time for these actuators is dependent on heat conduction and convection. For instance, an 860 µm multi-stranded coiled nylon actuator is limited to 0.2 Hz frequency of actuation, above which tensile stroke drops due to heat accumulation. We analyzed the thermal behavior of silver-coated nylon actuators and investigated the actuation under air flow, in hydrogel, and in water, to improve the frequency response. An improved frequency response was observed under air flow (compressed air) in relation to still air. The measured heat transfer coefficient under air flow reaches 137 W/m² /K enabling 5% strain at 0.8 Hz. The fastest frequency responses were observed in water and within hydrogel, where the nylon actuators demonstrated ~10% strain at 1 Hz (add water and hydrogel heat transfer coefficient). The application of a hydrogel coated actuator is demonstrated through an actuated 3D printed finger, which makes use of antagonistic coiled nylon actuators.